Divide by the smallest to give the ratio aproximately 1 Mg : 1 O. ![]() The ratio should be close to 1:1 as the formula of magnesium oxide is MgO.Having done this for both elements, they should find the ratio between the two by dividing them both by the smallest number.They should divide mass by the atomic mass for each element.They will also require the relative atomic masses. To find the formula of magnesium oxide, students will need the mass of the magnesium and the mass of the oxygen.having the magnesium coiled too tightly so that not all of it reactsįinding the formula of magnesium oxide Method one.not taring the balance correctly when measuring the mass.they may have prodded the product with their splint so not all of it got weighed (more common than you might expect).not all the magnesium may have reacted (the product may still look a bit grey rather than white).the magnesium oxide product may escape as they lift the lid.It is worth evaluating what they have done as there are several reasons why their results may be disappointing: Students sometimes get unconvincing results to this experiment. They could also calculate the increase in mass (mass 3 – mass 2), which corresponds to the mass of oxygen. This should allow them to calculate the mass of the mass of the magnesium (mass 2 – mass 1) and the mass of the product (mass 3 – mass 1). Students should have recorded the following masses: This is known as heating to constant mass. Repeat this step until the mass readings are consistent. Heat the crucible again for a couple of minutes and once again allow to cool.Re-weigh the crucible with lid containing the product (mass 3).Turn off the Bunsen burner and allow the apparatus to cool.Replace the lid if it appears that you are losing some product. At this point, remove the lid and heat for another couple of minutes. Keep heating and lifting the lid until you see no further reaction.If the lid is off for too long then the magnesium oxide product will begin to escape. You may see the magnesium begin to flare up. Once the crucible is hot, gently lift the lid with the tongs a little to allow some oxygen to get in.It is best to start with a gentle blue flame, but you will need to use a roaring flame (with the air hole fully open) to get the reaction to go. Light the Bunsen burner and begin to heat the crucible.Place the crucible containing the magnesium in the pipe clay triangle and put the lid on. Place the pipe clay triangle over the tripod in a Star of David formation, ensuring that it is secure. Set up the Bunsen burner on the heat resistant mat with the tripod.Weigh the crucible with the lid (mass 1) and then the magnesium inside the crucible with the lid (mass 2).If it is looking tarnished or black then clean it using the emery paper. Cut a piece of magnesium about 10–15 cm long. ![]() The apparatus and set up required to calculate the change on mass when magnesium burns If the magnesium is tarnished then emery or sand paper will be required to clean it. Fresh, clean magnesium is best for this experiment.
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